JPH0754888B2 - Bias circuit - Google Patents

Description

The present invention relates to a bias circuit for a high frequency circuit, and more particularly to a bias circuit for a high frequency multi-stage AB class bias amplifier.

[Conventional technology]

FIG. 3 shows an equivalent circuit of a conventional high frequency multi-stage class AB bias amplifier. In the figure, 1 is a high frequency transistor of the latter stage which is an active element of this amplifier, 2 is a high frequency transistor of the previous stage which is an active element which supplies a high frequency signal to the base of the transistor 1, and 3 includes DC blocking and properly transmits the high frequency signal. Matching circuits, 4 and 5 are front and rear bias circuits, and 6 and 7 are bias power supply terminals for supplying a bleeder current to the bias circuits 4 and 5. The bias circuit 4 is composed of a strip line 41, a high frequency bypass capacitor 42, a bias resistor 43 and a bias bleeder resistor 44, and the bias circuit 5 is a strip line.
51, a high frequency bypass capacitor 52, a bias resistor 53, and a bias bleeder resistor 54.

Next, the operation of the bias circuit configured as described above will be described with the bias circuit 4 in the preceding stage. Impedance Z (Ω) seen from bias circuit 4 from the base of transistor 2
When the impedance of the high frequency bypass capacitor 42 is regarded as “0” and the characteristic impedance of the strip line 41 is Z0 (Ω), Z = jZ0tan θl = jZ0tan (λg / 4) = ∞ (1) Therefore, When the bias circuit 4 is viewed from the base, it is open in terms of high frequency.

Next, the idle current (DC current when there is no signal) I _CQ2 of the transistor 2 is given as I _{CQ2 ≈I E} = I ₀ (ε ^qx −1) ··· (2), where x = V _EB / kT Become. However, I ₀ : Saturation current in the reverse direction q: Electron charge V _EB : Base-emitter voltage k: Boltzmann constant T: Absolute temperature. The base-emitter voltage V _EB is V _EB = V, where V _bb is the value of the DC voltage applied to the bias power supply terminal 6 and R1 and R2 are the values of the bias resistor 43 and the bias bleeder resistor 44. _bb・ R1 / (R1 ＋ R2) ・ ・ ・ ・ (3). However, the base current I _B << I _BB ≈ V _bb / (R1 + R2).

Based on the equations (1) to (3), the transistor 2 is turned on by setting the values R1 and R2 of the bias resistor 43 and the bias bleeder resistor 44, which are separated in terms of high frequency, according to the DC voltage _Vbb. The idle current I _CQ2 can be made to flow.

The above operation is the same in the case of the bias circuit 5.

[Problems to be solved by the invention]

In the high frequency circuit to which the conventional bias circuit is applied,
A bias circuit needs to be provided for each stage transistor, and a high frequency bypass capacitor, a bias resistor, and a bias bleeder resistor are required for each stage.
Therefore, as the number of stages increases, the number of parts increases and the space for the bypass circuit increases.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a bias circuit capable of supplying a base potential to each stage and reducing the number of components.

[Means for solving problems]

In order to achieve such an object, the present invention is provided with a strip line for separating active elements in a high frequency and a supply means for supplying a common base potential.

[Action]

In the present invention, a base potential common to each stage can be generated.

〔Example〕

FIG. 1 shows a high frequency multi-stage class AB bias amplifier in which one embodiment is applied to the bias circuit according to the present invention. In FIG. 1, 8 is a bias circuit, 9 is a bias power supply terminal, and the bias circuit 8 is a strip line 8 with an electrical length of λg / 4.
1a, 81b, high-frequency bypass capacitor 82, and bypass resistor
83 and bypass bleeder resistor 84. Also,
The bypass resistor 83 and the bypass bleeder resistor 84 form a supply means. In FIG. 1, the same or corresponding parts as those in FIG. 3 are designated by the same reference numerals.

Next, the operation of the amplifier having such a configuration will be described.
Since the bias circuit 8 is separated in high frequency by the strip lines 81a and 81b and the high frequency bypass capacitor 82, only the DC bias circuit in the amplifier is considered as shown in FIG. Where transistors 1 and 2
The emitter currents I _E1 and I _E2 are I _E1 = I _E2 = I _E , base-emitter voltage V _EB , thermal voltage V _T = kT / q, and reverse saturation current I ₀ , V _EB = V _T ln (I _E / I ₀ ) ... (4) The reverse saturation current I ₀ has the following relationship with the emitter-base junction area A.

I ₀ = γ _E A ··· (5) However, γ _E is a constant.

The emitter-base junction area of the transistor 1 A1, when the emitter-base junction area of the transistor 2 and A2, next _{I E1 / I E2 = A1 /} A2 ≒ I CQ1 / I CQ2, idle current I _CQ1, I _CQ2 is Transistor h _FE
Flow is proportional to the junction area of the transistor.

In this embodiment, the active element has been described in two stages.
The same effect is achieved no matter how many stages.

A diode may be used instead of the bias resistor 83.

〔The invention's effect〕

As described above, the present invention has the effect of reducing the number of parts by providing the strip line for separating the active elements in high frequency and the supply means for supplying the common base potential. Further, since the number of parts can be reduced, there is an effect that a space can be spared and simplification and compactness can be achieved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a high frequency multi-stage class AB bias amplifier to which an embodiment of the bias circuit according to the present invention is applied.
FIG. 3 is a circuit diagram showing the DC bias circuit, and FIG. 3 is a circuit diagram showing a high frequency multi-stage AB class bias amplifier to which a conventional bias circuit is applied. 1,2 ... Transistor, 3 ... Matching circuit, 8 ... Bias circuit, 9 ... Bias power supply terminal, 81a, 81b ... Strip line, 82 ... High frequency bypass capacitor, 83 ...
Bias resistor, 84 ... Bias bleeder resistor.

Claims (1)

[Claims] 1. A bias circuit for supplying a bias voltage from a common bias power supply to a high frequency circuit having a plurality of transistor circuits in a multi-stage configuration, wherein one end is connected to an input terminal of each transistor circuit, and between the common bias power supply and the transistors. And a common bias power source connected to the common connection point at the other end of each of the λ / 4 strip lines, and the emitter / base of each transistor. A bias circuit characterized in that the ratio of the junction area is made equal to the idle current ratio of each stage.